Device and method for post-treatment of exhaust gases of an internal combustion engine

ABSTRACT

An exhaust gas treatment device has a cylindrical body with axial passages having a catalyst and a central cavity. A filter is provided in the cavity and the cylindrical body is mounted for rotation in a housing through which the exhaust gas flows.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a device and method for post-treatmentof exhaust gases of an internal combustion engine, and in particularrelates to a device and method for post-treatment of soot particlesand/or nitrogen oxides in the exhaust gas stream.

[0002] Known NOx catalysts absorb nitrogen oxides produced during leanoperation of an engine and reduce accumulated NOx during rich operationof the engine, where the known methods are discontinuous andaccumulation and reduction of nitrogen oxides takes place at differenttimes. In order to be able to carry out such a method, the accumulatormust be emptied after a certain period of time because of its finiteabsorption capacity. This is done after a fixed predetermined time haselapsed or else the degree of fill of the catalyst must be determined.If the accumulator is regenerated after a fixed predetermined time, thishas the disadvantage that for safety reasons the accumulating capacityof the catalyst is not fully utilized, so that optimal engine operationwith regard to fuel consumption and exhaust gas behavior is notpossible. If the accumulator is regenerated when a given degree of fillof the accumulator has been reached, this has the disadvantage that anadditional device is required, to determine the degree of fill of theNOx-accumulating catalyst. There, exact determination of the degree offill of the accumulator is difficult, so that here too a switch toregenerative operation is made when the accumulator is not yetcompletely full. In the end, this likewise leads to less than optimaloperation of the engine. In addition, in both these methods optimalexhaust gas behavior is not obtained during rich operation of the engineand a complicated engine control system is required for cyclical engineoperation.

[0003] In addition, a minimum temperature of about 250° C. is requiredfor effective function of a NOx-accumulating catalyst. If the exhaustgas coming from the engine is too cold, the method can only functionwhen the catalyst is heated to this minimum temperature. Then heatlosses occur, as a result of which the energy requirement is greatlyincreased.

[0004] In addition, soot particles that should not be allowed to escapeinto the environment are present in the exhaust gas of diesel engines.For post-treatment of such exhaust gases carrying soot particles, in onewell known device the soot particles are retained and cyclically, as agiven degree of fill of the soot filter is reached, they are eitherremoved or the retained soot particles are ignited with a suitableheating device and burned. Both of these procedures are unsatisfactoryfor continuous use.

[0005] The object of the invention therefore is to develop a device andmethod for treatment of the exhaust gas stream of an internal combustionengine that permit optimal engine operation.

SUMMARY OF THE INVENTION

[0006] The device according to the invention for post-treatment ofexhaust gases of an internal combustion engine has a body or monolithwith channels through which the exhaust gas flows and which is arrangedto rotate in the exhaust gas stream. Here, a monolith is understood tomean a body that may consist of one piece that is made of ceramic, ofmetallic carrier materials or of ceramic or metallic segments, which arearranged in an accommodating support structure.

[0007] The device has an inflow channel that is in flow communicationwith a part (B1) of the channels of the body. Additionally provided is aflow connection that is in communication on the output side with thepart B1 of the channels approached by the inflow channel and connectssaid part with a part B2 of the channels that is not in flowcommunication with the inflow channel.

[0008] The body or monolith preferably is divided into two regions B1,B2, where the exhaust gas enters the first region B1 at the front faceof the body, exits at the rear face of the first region B1, flowsthrough the filter mounted there, enters a face of the second region B2and leaves the second region B2 at the other face, while during flow thebody rotates about an axis substantially perpendicular to the directionof flow of the exhaust gas stream.

[0009] The body preferably has a cylindrical shape, and the channelsextend in the radial direction. The body has a cylindrical recess in theaxial direction, in other words, the cylinder is hollow in the axialdirection. The body may consist of metal or ceramic, and may be built inone piece or of segments fitted together. If the body consists ofsegments, the latter are traversed by channels in such a way that afterthe segments are assembled the channels extend in the radial directionwith respect to the axis of symmetry of the cylinder.

[0010] The device preferably comprises a filter, which may be arrangedfor rotation, and the filter may in particular rotate with the monolith,while in the case of the cylindrical body with the axial recess thefilter is arranged in the latter. There, the filter may be stationary ormay rotate along with the body, where its speed of rotation need not beidentical to the speed of rotation of the body.

[0011] In addition, the internal combustion engine preferably has directfuel injection into the combustion chamber and/or is a diesel engine.

[0012] The filter preferably has a heating element that serves to bringthe filter to operating temperature after a cold start. When therequired temperature has been reached, the heating element may be shutoff. In principle, extra heating is provided only when engine conditions(exhaust gas temperature) do not lead to soot burnup.

[0013] In particular, the required temperature for pollutant conversionmay alternatively or secondarily also be rapidly obtained by suitablyselected engine parameters (injection quantity, injection course,reinjection), and here too the engine parameters are restored to theirnormal conditions when the desired temperature has been reached.

[0014] In addition, for pollutant reduction, in particular for thereduction of NOx, HC and/or CO, the body may be at least partiallycatalytically coated.

[0015] In addition, the device may have a stationary housing (10),having a chamber in which is arranged the body rotating about itslongitudinal axis. The housing preferably is made of a nonmetallicmaterial.

[0016] Rotation of the body preferably is effected by a drive unit. Thedrive unit may be an electric motor. It is alternatively possibly forthe drive unit to be formed by an outer magnetic field source andmagnets arranged within the housing. In addition, the body mayalternatively be rotated in the manner of a turbine by the exhaust gasstream. The speed of rotation of the body (4) preferably is about 0.3 to10 rpm, and the speed of rotation is selected so that the maximum of thetemperature distribution obtained remains within the body, preferably atthe site of the filter.

[0017] In addition, the device may have a means for the introduction ofadditional fuel in order to produce a reduction of the NOx exhaust gascomponent when the engine can be operated lean. The means forintroducing additional fuel is arranged in the axis of rotation of thebody.

[0018] The method according to the invention provides for post-treatmentof exhaust gases of an internal combustion engine, wherein a body isarranged in the exhaust gas stream, which body is traversed by channelsin the direction of flow of the exhaust gas and is divided into tworegions, has the following steps:

[0019] Passing of the exhaust gas stream into the front face of thefirst region,

[0020] Passing of the exhaust gas stream at the rear face of the firstregion into a face of a second region and discharge of the exhaust gasstream at the other face of the second region, and

[0021] Rotation of the body during operation about an axis, so that thechannels shift from the first region into the second region.

[0022] Preferably, the body is rotated about its axis at a speed suchthat heating of the second region by the exhaust gas stream leads toheating of the exhaust gas stream through the first region.

[0023] Soot particles in the exhaust gas stream preferably are retainedin a filter, which is arranged between the exhaust gas outlet-side faceof the first region and the exhaust gas inlet-side face of the secondregion, and the speed of rotation is selected so that the maximum of thetemperature region is located approximately at the filter.

[0024] The body used in the method preferably is at least partiallycatalytically coated, so that NOx accumulation of the exhaust gas iseffected during the lean phases of internal combustion engine operation.A continuous NOx-accumulating regeneration method can be effected byaddition of reducing agents into the body.

[0025] The method according to the invention for desulfurization of thedevice according to the invention for post-treatment of exhaust gases ofan internal combustion engine, where the device is designed as a NOxaccumulator, has the following steps:

[0026] at the start of desulfurization retardation or interruption ofrotation of the body, with simultaneous increase of pollutant quantityin the exhaust gas, until a resulting temperature maximum has migratedinto or through the second region, in particular near the exhaust gasexit-side face of the second region,

[0027] rotation of the body until the second region at leastpredominantly assumes the place of the first region, so that thetemperature maximum lies predominantly in the first region, andinterruption of rotation until the temperature maximum has moved into atleast the relocated first region,

[0028] reduction of reinjection and restored rotation of the body.

[0029] At the same time it may be necessary for retardation orinterruption of rotation to be repeated a number of times, until allregions have been substantially desulfurized. Continuous rotation of thebody is resumed when the temperature maximum is located at approximatelythe interface of the two regions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1a shows a horizontal cross-sectional view through a firstembodiment of the device according to the invention for post-treatmentof the exhaust gas of an internal combustion engine.

[0031]FIG. 1b shows a vertical cross section through the device of FIG.1a.

[0032]FIG. 2a shows horizontal cross-sectional view through a secondembodiment of the device according to the invention for post-treatmentof the exhaust gas of an internal combustion engine.

DESCRIPTION OF THE INVENTION

[0033]FIG. 1a shows a horizontal cross section through a first preferredembodiment of a device according to the invention for post-treatment ofthe exhaust gas of an internal combustion engine. A cylindrical body isarranged in a chamber within a housing 10. Untreated exhaust gas of anengine (not illustrated) flows through an exhaust gas inlet 1 in to anouter face 2 of a first region B1 of a cylindrical body 4 that istraversed by channels 3. Channels 3 run in the radial direction withrespect to the axis of rotation 9 formed by the axis of symmetry of thecylinder. The channels 3, arranged perpendicular to the axis of rotation9, are at least partially catalytically coated, as has already beendescribed above. After exit of the exhaust gas from the inner face 5 ofthe body 4, which forms an axial cavity 7 located centrally in the body,the exhaust gas goes through a particle filter 6 arranged in the cavity7, through the inner face 5, enters an opposite second region B2, leavesregion B2 through outer face 2 and enters a discharge channel 8. In FIG.1a, it is shown that the first region and the second region are eachlimited to 3 channels by the inflow channel 1 and the discharge channel8. This is not mandatory. In another design of the housing 10surrounding the body 4, the waste gas flowing in and out in eachinstance reaches a first and second region B1, B2 of at most 180°. Inother words, the first and second region may comprise at most one-halfof the body 4.

[0034]FIG. 1b shows a vertical section through the device according tothe invention. The filter 6, which in general rotates synchronously withthe body 4, is arranged in the interior cavity of the body 4 which istraversed by channels 3. The body 4 and the filter 6 are arranged in achamber formed by a suitable housing 10. Rotation takes place about anaxis of rotation 9, which may serve as inlet for additional fuel forcombustion in a catalytically active filter or in the rotor matrix,i.e., the body 4.

[0035] Owing to flow through the body 4 with the filter 6, thetemperature rises at the inlet side due to catalytic conversion of COand HC present in the exhaust gas during passage through thecatalytically coated channels 3. At the same time, nitrogen oxides canbe absorbed chemically if the channels 3 are coated with a NOx-absorbingcatalyst. The temperature maximum is reached in the center of thedevice, in the particle filter 6. Upon continued passage through thebody 4 or rotor the exhaust gas again gives off its heat and leaves therotor 4 at about the same temperature as on the inlet side. Withoutrotation the temperature front, i.e., the maximum temperature, would bedriven out of the device. Owing to rotation of the rotor 4 thetemperature front is always driven back into the system. A periodicallystationary temperature profile, whose maximum lies in the region of thefilter 6, is produced in the body.

[0036]FIG. 2 shows a horizontal cross-sectional view through a secondembodiment of the device according to the invention for post-treatmentof exhaust gases of an internal combustion engine, in which the deviceis operated as a pure NOx-accumulating catalyst.

[0037]FIG. 2 shows a body 4, rotating about its longitudinal axis, whichis coated as a NOx-accumulating catalyst and which is used as aregenerative heat exchanger. The body 4 has a great plurality of finechannels 3 in the radial direction and exhaust gases flow through itradically, specifically, exhaust gases are supplied to it through aninflow channel 1 and are carried away through a discharge channel 8,whereby first and second regions B1, B2 are formed as in the case of thefirst embodiment. In addition, the body has an axial cavity 7, which isbounded by the inner face 5 of the body 4. The axial cavity serves forflow communication of the channels 3 of the first and of the secondregion B1, B2. Advantageously, no flow deflection takes place, wherebypressure loss is kept low. The inner part of the channels 3, representedas a ring-shaped area T1, is coated with a NOx-accumulating catalyst.The outer part of the channels, represented by a ring-shaped area T2, isnot coated and does not participate in catalysis, having the functiononly of heat exchange. The radial flow with simultaneous rotation allowsa temperature profile to be established in the body 4, which at theinlet and outlet sides of the outer face 2 of the body is at aboutexhaust gas temperature and toward the center rises steeply to about 350to 400° C. As a result, part of the catalyst is always in an optimaltemperature region for NOx accumulation. The rotating arrangement of thecatalyst, i.e., the body 4, provides for best possible heat recovery bythe regeneration principle. With ideal heat insulation and correctdimensioning and rotational speed, the heat once brought in will notleave the system. The heat losses actually occurring are offset by theheat of reaction that is released upon pollutant oxidation in the regionT1.

[0038] For starting up the cold system, the ignition temperature ofabout 200° C. must be reached in the catalytically active region T2. Forthis purpose, an electric heating element 11 may be provided in thecenter of the body 4. Alternatively and/or secondarily, the temperaturerequired for pollutant conversion may also be obtained by suitablyselected engine parameters (particularly in the case of common-railinjection, for example, by variation of injection timing, injectioncourse, injection quantity, and/or reinjection). After the ignitiontemperature has been reached, such measures are ended. Additionaltemperature increase takes place only through a brief increase inpollutant concentrations, which raises the catalyst temperature throughthe heat of reaction released upon conversion of pollutants in theregion T1. This increase in pollutant concentration may take placeeither through separate fuel introduction in the center of the body 4,or may also be brought about through modifications of engine parameters.

[0039] Rotation of the body 4 is realized by a suitable electric ormechanical drive (not represented). For this purpose, the body 4 ismounted on a shaft rotatable about its axis of rotation 9, which is putinto rotation by the abovementioned drive. The additional introductionof fuel may also be effected through this shaft 9. When an electricmotor is used, the speed of rotation may be adapted to the operatingcondition of the vehicle engine by means of suitable information fromthe engine-control device. In addition, the body 4 is arranged in asuitable stationary housing 10.

[0040] Regeneration of the NOx-accumulating catalyst is effected inknown fashion by engine enrichment of the exhaust gas.

[0041] When sulfurous fuel is used, desulfurization of the catalyst mustbe carried out from time to time, as has already been described above.This is done thermally at temperatures above 600° C. As alreadymentioned above, in the system described a temperature rise of almostany degree may be obtained by increasing the concentration of pollutantor by its oxidation. By appropriate control of the speed of rotation andpollutant concentration, the catalyst can be kept at the necessary hightemperatures for the required time of several minutes. As alreadydescribed above, the consumption of energy is distinctly lower than inconventional systems.

[0042] Therefore, the following embodiments of the device describedabove by means of two examples are possible:

[0043] Device with a body 4, capable of rotation in the exhaust gasstream, without catalytic coating and without filter, for producing atemperature maximum in the device;

[0044] Device with a body 4, capable of rotation in the exhaust gasstream and a filter 6 arranged in the body 4, for burnup of sootparticles;

[0045] Device with a body 4, capable of rotation in the exhaust gasstream and having an at least partial catalytic coating of the body 4;

[0046] Device with a body 4, capable of rotation in the exhaust gasstream, as well as a filter 6 arranged in the body 4, and having an atleast partial catalytic coating of the body.

[0047] While there has been described what are believed to be thepreferred embodiment of the present invention, those skilled in the artwill recognize that other and further changes and modifications may bemade thereto without departing from the spirit of the invention, and itis intended to claim all such changes and modifications as fall withinthe true scope of the invention.

LIST OF REFERENCE NUMERALS

[0048]1 Inflow channel

[0049]2 Outer face

[0050]3 Channels

[0051]4 Body or rotor

[0052]5 Inner face

[0053]6 Filter

[0054]7 Axial cavity

[0055]8 Discharge channel

[0056]9 Axis of rotation

[0057]10 Housing

[0058]11 Electric heating element

[0059] B1 First region

[0060] B2 Second region

[0061] T1 Inner ring-shaped area

[0062] T2 Outer ring-shaped area

In the claims:
 1. Apparatus for treatment of exhaust gases of aninternal combustion engine comprising a housing having a gas inlet and agas outlet and a chamber arranged between said inlet and said outlet, agas permeable body at least partially coated with a catalyst forreduction of pollutant gases, and arranged for rotation in said chamberabout an axis transverse to a direction corresponding to flow of gasbetween said inlet and said outlet, said gas permiable body having acentral cavity having a filter arranged therein, said gas permeable bodybeing arranged in said chamber such that gases entering said gas inletflow through a first region of said body, through said filter in saidcentral cavity and through a second region of said body to said gasoutlet.
 2. Apparatus as specified in claim 1 wherein said gas inlet ofsaid housing is in flow communication with channels in said first regionof said body.
 3. Apparatus as specified in claim 1 wherein said filteris arranged to rotate with said body.
 4. Apparatus as specified in claim1 wherein said body has a cylindrical shape and includes radiallyextending gas flow channels.
 5. Apparatus as specified in claim 4wherein said cavity comprises a cylindrical recess extending along theaxis of said cylindrical body.
 6. Apparatus as specified in claim 1further including a heating element.
 7. Apparatus as specified in claim1 wherein said body is arranged to rotate about a cylindrical axiswithin said housing.
 8. Apparatus as specified in claim 7 , wherein saidhousing is made of a nonmetallic material.
 9. Apparatus as specified inclaim 1 wherein said body is rotated by a drive unit.
 10. Apparatus asspecified in claim 9 , wherein said drive unit is an electric motor. 11.Apparatus as specified in claim 9 , wherein said drive unit is formed byproviding an magnetic field and magnets arranged within the housing. 12.Apparatus as specified in claim 1 wherein said body is arranged torotate a speed of about 0.3 to 10 rpm.
 13. Apparatus as specified inclaim 1 wherein said body comprises ceramic.
 14. Apparatus as specifiedin claim 1 wherein said body is fabricated using metal.
 15. Apparatus asspecified in claim 1 wherein said body is a monolith.
 16. Apparatus asspecified in claim 1 wherein said body comprises segments that aretraversed by channels.
 17. Apparatus as specified in claim 1 furtherincluding an inlet for the introduction of additional fuel. 18.Apparatus as specified in claim 17 wherein said inlet apparatus for theintroduction of additional fuel is arranged at the axis of rotation ofthe body.
 19. A method for post-treatment of an exhaust gust gas streamof an internal combustion engine comprising: providing a body having acatalyst in portions thereof and having a cavity with a filter; passingsaid exhaust gas through channels in a first region of said body,through said filter and through channels a second region of said bodywhereby soot particles are retained in said filter; and rotating saidbody to interchange said first and second regions of said body.
 20. Amethod as specified in claim 19 wherein said body is rotated at a speedwhich causes a maximum temperature region of said body to be located atsaid filter thereby to cause combustion of said soot particles.
 21. Amethod as specified in claim 19 wherein reducing agents are added tocause continuous reduction of Nox accumulation in said body.
 22. Amethod as specified in claim 19 further providing desulfurigation ofsaid body, comprising periodically increasing the pollutant quantity ofsupplied exhaust gas and retarding or interrupting rotation of said bodyuntil a maximum temperature region is in said second region, and whereinsaid body is thereafter rotated so that second region assumes theoriginal position of said first region and said maximum temperatureregion is predominantly in said repositioned first region and thereafterreducing the pollutant quantity.
 23. Method according to claim 22 ,wherein said retardation or interruption of rotation is repeated anumber of times, until said body is substantially desulfurized. 24.Method according to claim 22 , wherein that continuous rotation of saidbody is resumed when the temperature maximum is located at approximatelythe interface of the first and second regions.